Lead frame structure and packaging method

Abstract

The present invention provides a lead frame structure and packaging method, wherein the lead frame structure includes a lead frame and a plurality of transverse connecting ribs provided on the lead frame, and a plurality of longitudinal connecting ribs perpendicular to the transverse connecting ribs. The transverse connecting ribs and the longitudinal connecting ribs separate the lead frame into a plurality of lead frame unit groups, each of which includes at least two transversely adjacent lead frame units. Each lead frame unit includes a base island and pins provided on a longitudinal side of the base island and separated from the base island. The pins of the same group of lead frame units share a common connecting rib, the two ends of the common connecting rib are respectively connected to the longitudinal connecting rib, and the portion of the common connecting rib close to the longitudinal connecting rib is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located. The lead frame structure of the present invention is compatible with multiple packaging methods.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit packaging, in particular to a lead frame structure and a packaging method using the lead frame structure. Background Art

[0002] In the field of power devices, there is a package called LFPAK, which originated from abroad and has been around for 20 years. Figure 1 As shown, the LFPAK package assembly process is as follows: First, the chip 130 is soldered to the base island 110 of the lead frame 100. The lead frame 100's snap 120 and copper clip 140 are then used to position the package and complete the assembly. Next, the lead frame 100 is encapsulated with a plastic encapsulation 150. Finally, the ribs are trimmed and the pins are bent. This product features curved pins that absorb stress after mounting on the PCB, preventing cracking in the plastic encapsulation.

[0003] Disadvantages of the existing LFPAK packaging structure:

[0004] 1. The copper clip 140 and lead frame 100 are positioned in the X and Y directions using the snap 120. Due to processing errors between the various components, the snap 120 can fail. Interference mismatches can cause the copper clip to fail to secure, preventing the product from being injection molded and resulting in scrap. Excessive freedom can cause the mold to press against the pins, or the rib cutting mold to cut off the pins.

[0005] 2. This structure uses an integrated design of the copper clip 140 and the pins. After assembly, the copper clip is directly above the lead frame base island. As a result, this structure can only be used for copper clip type packaging and cannot be used for low-cost aluminum ribbon bonding packaging on the market.

[0006] 3. Since this structure uses a snap-fit ​​to fix the relative position of the copper clip and the lead frame, the snap-fit ​​design area wastes material and frame area, resulting in a relatively high unit price of this product. Summary of the Invention

[0007] An object of the present invention is to provide a lead frame structure compatible with multiple packaging methods and a packaging method using the lead frame structure.

[0008] In an embodiment of the present invention, a lead frame structure is provided, which includes a lead frame and a plurality of transverse connecting ribs arranged on the lead frame and a plurality of longitudinal connecting ribs perpendicular to the transverse connecting ribs. The transverse connecting ribs and the longitudinal connecting ribs separate the lead frame into a plurality of lead frame unit groups. Each lead frame unit group includes at least two transversely adjacent lead frame units. Each lead frame unit includes a base island and pins arranged on a longitudinal side of the base island and separated from the base island. The pins of the same group of lead frame units share a common connecting rib. The two ends of the common connecting rib are respectively connected to the longitudinal connecting ribs. The part of the common connecting rib close to the longitudinal connecting rib is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located.

[0009] In the embodiment of the present invention, the height of the plane where the pins are located is equal to the height of the top surface of the chip after the base island is welded to the chip.

[0010] In an embodiment of the present invention, the tip ends of the plurality of pins are pre-cut and disconnected from the frame body.

[0011] In an embodiment of the present invention, one transverse side of the base island is connected to the longitudinal connecting reinforcement via a transverse support rod, and the other transverse side of the base island is connected to a T-shaped support rod, and the T-shaped support rod is connected to the transverse connecting reinforcement.

[0012] In an embodiment of the present invention, a packaging method for the lead frame structure is provided, which includes:

[0013] Soldering the chip onto the base island;

[0014] welding a copper clip on the chip and the pin so that the chip and the pin are electrically connected through the copper clip;

[0015] Injection molding: encapsulating the chip, the pins, and the copper clip, and tinning the exposed parts after the encapsulation;

[0016] electroplating, tinning the exposed portion of the pin;

[0017] Cut the ribs of the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip;

[0018] The pins of the chip are bent and formed.

[0019] In an embodiment of the present invention, another packaging method of the lead frame structure is provided, which includes:

[0020] Soldering the chip onto the base island;

[0021] Bonding aluminum ribbons and copper wires on the chip and the pins, so that the chip and the source pin are electrically connected through the aluminum ribbon, and the chip and the gate pin are electrically connected through the copper wire;

[0022] Injection molding: encapsulating the chip, the pins, the aluminum tape, and the copper wire, and tinning the exposed parts after the encapsulation;

[0023] Cut the ribs of the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip;

[0024] The pins of the chip are bent and formed.

[0025] Compared with the prior art, the lead frame structure of the present invention is adopted, and each lead frame unit group includes at least two laterally adjacent lead frame units, and each lead frame unit includes a base island and a pin arranged on a longitudinal side of the base island and separated from the base island. The pins of the same group of lead frame units share a common connecting rib, and the two ends of the common connecting rib are respectively connected to the longitudinal connecting rib. The part of the common connecting rib close to the longitudinal connecting rib is bent and convex upward, so that the plane where the pins are located is higher than the plane where the base island is located, so that after the chip is installed, the plane where the chip is located is aligned with the plane where the chip is located. The height of the plane where the pins are located is flush, which facilitates direct welding of copper clips or bonding of aluminum strips and copper wires, thereby supporting two different packaging methods; in addition, since the tip ends of the multiple pins are pre-cut and disconnected from the frame body, the tip end surfaces of the pins will also be covered with tin during electroplating, thereby enhancing the bonding strength between the packaged product and the PCB board; support rods are provided on the left and right sides of the base island, so that the mold can press the support rods to prevent glue overflow from the exposed base island surface during plastic sealing; there is no need to use clips to fix the copper clips, which saves frame area and materials, thereby supporting the formation of more lead frame units in a frame of the same size. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of a process of packaging using a lead frame of the prior art.

[0027] Figure 2 1 is a schematic diagram of the overall structure of the lead frame structure of an embodiment of the present invention.

[0028] Figure 3 It is a partial structural diagram of the lead frame structure of an embodiment of the present invention.

[0029] Figure 4 yes Figure 3 Schematic diagram of the cross section along line AA.

[0030] Figure 5 The present invention is a schematic diagram of a packaging process using a lead frame structure according to an embodiment of the present invention.

[0031] Figure 6 It is another schematic diagram of a packaging process using the lead frame structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] The implementation of the present invention is described in detail below with reference to specific embodiments.

[0034] like Figure 2 and Figure 3 As shown, in an embodiment of the present invention, a lead frame structure is provided, which includes a lead frame 200 and a plurality of transverse connecting ribs 210 arranged on the lead frame 200, and a plurality of longitudinal connecting ribs 220 perpendicular to the transverse connecting ribs. The transverse connecting ribs 210 and the longitudinal connecting ribs 220 separate the lead frame into a plurality of lead frame unit groups 230. Each lead frame unit group 230 includes two transversely adjacent lead frame units 240. It should be noted that, in other embodiments of the present invention, each lead frame unit group 230 may include three or more transversely adjacent lead frame units 240, and the specific number depends on actual needs, and the present invention does not limit this.

[0035] Each lead frame unit 240 includes a base island 241 and a plurality of pins 242 disposed on a longitudinal side of the base island 241 and separated from the base island 241. The pins 242 of the same group of lead frame units share a common connecting rib 243, the two ends of which are respectively connected to the longitudinal connecting rib 220.

[0036] like Figure 4 As shown, the portion of the common connecting rib 243 near the longitudinal connecting rib 220 is bent and raised upward, so that the plane where the pins 242 are located is higher than the plane where the base island 241 is located. Specifically, by adjusting the amplitude of the bend and raise, the height of the plane where the pins 242 are located can be equal to the height of the top surface of the chip after the chip is soldered to the base island 241. This ensures that when soldering a copper clip or bonding an aluminum ribbon, the contact surface of the copper clip / aluminum ribbon, the chip surface, and the pins 242 are on the same plane, thereby achieving a more reliable electrical connection.

[0037] Furthermore, in this embodiment of the present invention, the tip ends 2421 of the plurality of pins 242 are pre-cut and disconnected from the frame body. This arrangement allows the plurality of pins 242 to be suspended in the air. Simply by bending the common connecting rib 243, the pins 242 can be moved upwards, facilitating the upward movement of the entire pin 242. Furthermore, during the tinning process after the chip is plastic-encapsulated, since the tip ends 2421 of the plurality of pins 242 are pre-cut and exposed, these tip ends 2421 are also tinned, thereby enhancing the bonding strength between the packaged product and the PCB board.

[0038] In this embodiment of the present invention, one transverse side of the base island 241 is connected to the longitudinal connecting rib 220 via a transverse support rod 244, and the other transverse side of the base island 241 is connected to a T-shaped support rod 245, which is connected to the transverse connecting rib 210. This arrangement provides support rods on both the left and right sides of the base island 241, facilitating the mold to press against the support rods during molding to prevent glue overflow from the exposed base island surface.

[0039] like Figure 5 As shown, in an embodiment of the present invention, a packaging method using the above lead frame structure is also provided, which includes the following steps:

[0040] Soldering the chip 300 onto the base island 241;

[0041] Soldering a copper clip 400 on the chip 300 and the pin 242 so that the chip 300 and the pin 242 are electrically connected via the copper clip 400 ;

[0042] Injection molding to encapsulate the chip 300, the pins 242, and the copper clip 400, and tin the exposed portions after the encapsulation;

[0043] Cut the ribs on the lead frame after plastic encapsulation to separate each plastic encapsulated chip and each pin of the chip;

[0044] The pins of the chip are bent and formed.

[0045] like Figure 6 As shown, in an embodiment of the present invention, another packaging method using the above-mentioned lead frame structure is also provided, which includes the following steps:

[0046] Soldering the chip 300 onto the base island 241;

[0047] Bonding an aluminum ribbon 500 and a copper wire 600 to the chip 300 and the pin 242 , so that the chip 300 and the source pin 242 are electrically connected through the aluminum ribbon 500 , and the chip 300 and the gate pin 242 are electrically connected through the copper wire 600 ;

[0048] Injection molding to encapsulate the chip 300, the pins 242, the aluminum tape 500, and the copper wire 600, and tin the exposed portions after the encapsulation;

[0049] Cut the ribs of the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip;

[0050] The pins of the chip are bent and formed.

[0051] In summary, the lead frame structure of the present invention is adopted, and each lead frame unit group includes at least two laterally adjacent lead frame units, and each lead frame unit includes a base island, and a pin arranged on a longitudinal side of the base island and separated from the base island. The pins of the same group of lead frame units share a common connecting rib, and the two ends of the common connecting rib are respectively connected to the longitudinal connecting rib, and the part of the common connecting rib close to the longitudinal connecting rib is bent and convex upward, so that the plane where the pins are located is higher than the plane where the base island is located, so that after the chip is installed, the plane where the chip is located is aligned with the pins. The height of the plane is flush, which is convenient for directly welding copper clips or bonding aluminum strips and copper wires, thereby supporting two different packaging methods; in addition, since the tip ends of the multiple pins are pre-cut and disconnected from the frame body, the tip ends of the pins will also be covered with tin during electroplating, thereby enhancing the bonding strength between the packaged product and the PCB board; support rods are provided on the left and right sides of the base island, so that the mold can press the support rods to prevent glue overflow from the exposed base island surface during plastic sealing; there is no need to use a buckle to fix the copper clip, which saves frame area and material, thereby supporting the formation of more lead frame units in a frame of the same size.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lead frame structure, characterized in that: The lead frame includes a lead frame and a plurality of transverse connecting ribs arranged on the lead frame and a plurality of longitudinal connecting ribs perpendicular to the transverse connecting ribs. The transverse connecting ribs and the longitudinal connecting ribs separate the lead frame into a plurality of lead frame unit groups. Each lead frame unit group includes at least two transversely adjacent lead frame units. Each lead frame unit includes a base island and pins arranged on a longitudinal side of the base island and separated from the base island. The pins of the same group of lead frame units share a common connecting rib. The two ends of the common connecting rib are respectively connected to the longitudinal connecting ribs. The part of the common connecting rib close to the longitudinal connecting rib is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located. The height of the plane where the pins are located is equal to the height of the top surface of the chip after the chip is welded to the base island.

2. The lead frame structure according to claim 1, wherein: The tip ends of the pins are pre-cut and separated from the lead frame.

3. The lead frame structure according to claim 1, wherein: One transverse side of the base island is connected to the longitudinal connecting reinforcement via a transverse support rod, and the other transverse side of the base island is connected to a T-shaped support rod, and the T-shaped support rod is connected to the transverse connecting reinforcement.

4. A packaging method using the lead frame structure according to any one of claims 1 to 3, characterized in that: include: Soldering the chip onto the base island; welding a copper clip on the chip and the pin so that the chip and the pin are electrically connected through the copper clip; Injection molding: encapsulating the chip, the pins, and the copper clip, and tinning the exposed parts after the encapsulation; electroplating, tinning the exposed portion of the pin; Cut the ribs of the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

5. A packaging method using the lead frame structure according to any one of claims 1 to 3, characterized in that: include: Soldering the chip onto the base island; Bonding aluminum ribbons and copper wires on the chip and the pins, so that the chip and the source pin are electrically connected through the aluminum ribbon, and the chip and the gate pin are electrically connected through the copper wire; Injection molding: encapsulating the chip, the pins, the aluminum tape, and the copper wire, and tinning the exposed parts after the encapsulation; Cut the ribs of the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

Images